Various systems have been used for measuring the DC characteristics of both active and passive electrical devices. Conventionally, in such systems a DC current is applied directly to a device and an output DC voltage is measured; or a DC voltage is directly applied and an output DC current is measured.
For measuring the DC characteristics of semiconductor devices the classical measuring instrument is the curve tracer in which a DC voltage (or current) is applied to the device under test (hereinafter referred to as a DUT) and the resulting output current (or voltage) is displayed by means of analog circuitry on a cathode ray tube (CRT). The curve tracer, unfortunately, suffers from several limitations: first, since the results are displayed in analog form on a CRT it is generally difficult to accurately read the displayed data; second, in order to change the type of measurement desired, such as required to measure the various parameters of a transistor, it is necessary to physically alter or exchange the measuring circuit itself; and third, such a system has no means for the direct storage of the measured results.
Generally, in such a conventional system, when automation is desired, a computer is employed for controlling matrix switches which in turn make connection between a plurality of voltage sources, current sources, voltmeters and ammeters and the various terminals of the DUT. Such a system has proven very useful, but is bulky, complex, and expensive. In addition, it has proven difficult to rapidly perform a wide range of desired measurements.